Two negative HPT's, no period?

I am a little uneasy right now...I have endometriosis and have been on NuvaRing with much success and then had an appendectomy in August which also showed an ovarian cyst that ruptured. Since then, my periods have started a little later than usual and has caused me to mess up the timing of putting new rings in. I had a follow up ultrasound (from the surgery) that showed everything was fine. On Dec 8th...after not starting when I should have, we did another ultrasound and everything was fine...I started just a couple of days after the ultrasound and started a new ring but then started spotting/bleeding again about a week into the ring- this was early January. I did take the ring out in thinking I would wait until I have a 'real' period for sure to restart a new ring and start calculations correctly from that point...but I have not had a period yet, it has been two months without a ring in for the suggested 3 weeks- the last ring was in for about 1 or 2 weeks in late Dec/early Jan. I have had some nausea but not much, I have an increase in urination and am tired, but this could just be in my head. I have taken 2 HTP -3days apart- and they both came back negative. Not knowing when I actually need to start makes me wonder if I might be pregnant but testing too early. But if I was pregnant, could I be exhibiting symptoms before a positive HTP? I would appreciate any advice or others stories that are similar to mine!